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<jats:title>The Holy GRAIL?</jats:title> <jats:p> The gravity field of a planet provides a view of its interior and thermal history by revealing areas of different density. GRAIL, a pair of satellites that act as a highly sensitive gravimeter, began mapping the Moon's gravity in early 2012. Three papers highlight some of the results from the primary mission. <jats:bold> Zuber <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6120" page="668" related-article-type="in-this-issue" vol="339" xlink:href="10.1126/science.1231507">668</jats:related-article> , published online 6 December) discuss the overall gravity field, which reveals several new tectonic and geologic features of the Moon. Impacts have worked to homogenize the density structure of the Moon's upper crust while fracturing it extensively. <jats:bold> Wieczorek <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6120" page="671" related-article-type="in-this-issue" vol="339" xlink:href="10.1126/science.1231530">671</jats:related-article> , published online 6 December) show that the upper crust is 35 to 40 kilometers thick and less dense—and thus more porous—than previously thought. Finally, <jats:bold> Andrews-Hanna <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6120" page="675" related-article-type="in-this-issue" vol="339" xlink:href="10.1126/science.1231753">675</jats:related-article> , published online 6 December) show that the crust is cut by widespread magmatic dikes that may reflect a period of expansion early in the Moon's history. </jats:p>

<jats:title>The Holy GRAIL?</jats:title> <jats:p> The gravity field of a planet provides a view of its interior and thermal history by revealing areas of different density. GRAIL, a pair of satellites that act as a highly sensitive gravimeter, began mapping the Moon's gravity in early 2012. Three papers highlight some of the results from the primary mission. <jats:bold> Zuber <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6120" page="668" related-article-type="in-this-issue" vol="339" xlink:href="10.1126/science.1231507">668</jats:related-article> , published online 6 December) discuss the overall gravity field, which reveals several new tectonic and geologic features of the Moon. Impacts have worked to homogenize the density structure of the Moon's upper crust while fracturing it extensively. <jats:bold> Wieczorek <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6120" page="671" related-article-type="in-this-issue" vol="339" xlink:href="10.1126/science.1231530">671</jats:related-article> , published online 6 December) show that the upper crust is 35 to 40 kilometers thick and less dense—and thus more porous—than previously thought. Finally, <jats:bold> Andrews-Hanna <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6120" page="675" related-article-type="in-this-issue" vol="339" xlink:href="10.1126/science.1231753">675</jats:related-article> , published online 6 December) show that the crust is cut by widespread magmatic dikes that may reflect a period of expansion early in the Moon's history. </jats:p>

<jats:title>The Holy GRAIL?</jats:title> <jats:p> The gravity field of a planet provides a view of its interior and thermal history by revealing areas of different density. GRAIL, a pair of satellites that act as a highly sensitive gravimeter, began mapping the Moon's gravity in early 2012. Three papers highlight some of the results from the primary mission. <jats:bold> Zuber <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6120" page="668" related-article-type="in-this-issue" vol="339" xlink:href="10.1126/science.1231507">668</jats:related-article> , published online 6 December) discuss the overall gravity field, which reveals several new tectonic and geologic features of the Moon. Impacts have worked to homogenize the density structure of the Moon's upper crust while fracturing it extensively. <jats:bold> Wieczorek <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6120" page="671" related-article-type="in-this-issue" vol="339" xlink:href="10.1126/science.1231530">671</jats:related-article> , published online 6 December) show that the upper crust is 35 to 40 kilometers thick and less dense—and thus more porous—than previously thought. Finally, <jats:bold> Andrews-Hanna <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6120" page="675" related-article-type="in-this-issue" vol="339" xlink:href="10.1126/science.1231753">675</jats:related-article> , published online 6 December) show that the crust is cut by widespread magmatic dikes that may reflect a period of expansion early in the Moon's history. </jats:p>

<jats:title>Acid-Derived Diversity</jats:title> <jats:p> Compounds with nitrogen-bearing rings have proven rather promising in pharmaceutical research, spurring the need for improved synthetic methods to access structurally diverse variants of this motif. <jats:bold> Duttwyler <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6120" page="678" related-article-type="in-this-issue" vol="339" xlink:href="10.1126/science.1230704">678</jats:related-article> ) show that applying acids of different strengths to a dihydropyridine intermediate leads to selective protonation at either of two sites, depending on whether the reaction proceeds under kinetic or thermodynamic (that is, equilibrated) control. The protonations in turn activate the rings for addition of various carbon nucleophiles to the periphery, thereby affording multiple different substitution patterns for use in screening studies. </jats:p>

<jats:title>Mimicking Hydrogenase</jats:title> <jats:p> Hydrogenase enzymes possess unusual bimetallic active sites that cleave H <jats:sub>2</jats:sub> . The enzymes make use of abundant metals (iron and sometimes nickel), in contrast to the often expensive synthetic catalysts that rely on rarer elements such as ruthenium or platinum. <jats:bold> Ogo <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6120" page="682" related-article-type="in-this-issue" vol="339" xlink:href="10.1126/science.1231345">682</jats:related-article> ; see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6120" page="658" related-article-type="in-this-issue" vol="339" xlink:href="10.1126/science.1233210">Armstrong</jats:related-article> </jats:bold> ) now report a bimetallic coordination compound of iron and nickel that can catalyze electron and hydride transfers from H <jats:sub>2</jats:sub> in a manner analogous to the corresponding enzyme and characterize the structure of an intermediate with bound hydride. </jats:p>

<jats:title>Impact Dating</jats:title> <jats:p> The large mass extinction of terrestrial and marine life—most notably, non-avian dinosaurs—occurred around 66 million years ago, at the boundary between the Cretaceous and Paleogene periods. But attributing the cause to a large asteroid impact depends on precisely dating material from the impact with indicators of ecological stress and environmental change in the rock record. <jats:bold> Renne <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6120" page="684" related-article-type="in-this-issue" vol="339" xlink:href="10.1126/science.1230492">684</jats:related-article> ; see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6120" page="655" related-article-type="in-this-issue" vol="339" xlink:href="10.1126/science.1233948">Pälike</jats:related-article> </jats:bold> ) acquired high-precision radiometric dates of stratigraphic layers surrounding the boundary, demonstrating that the impact occurred within 33,000 years of the mass extinction. The data also constrain the length of time in which the atmospheric carbon cycle was severely disrupted to less than 5000 years. Because the climate in the late Cretaceous was becoming unstable, the large-impact event appears to have triggered a state-shift in an already stressed global ecosystem. </jats:p>

<jats:title>Stressed Out</jats:title> <jats:p> Large seismic events such as the 2011 magnitude 9.0 Tohoku-Oki earthquake can have profound effects not just on the severity of ground motion and tsunami generation, but also on the overall state of the crust in the surrounding regions. <jats:bold> Lin <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6120" page="687" related-article-type="in-this-issue" vol="339" xlink:href="10.1126/science.1229379">687</jats:related-article> ) analyzed the stress 1 year after the Tohoku-Oki earthquake and compared it with the estimated stress state before the earthquake. In situ resistivity images were analyzed from three boreholes drilled into the crust across the plate interface where the earthquake occurred. Stress values indicate a nearly complete drop in stress following the earthquake such that the type of faulting above the plate boundary has changed substantially. These findings are consistent with observations that the sea floor moved nearly 50 meters during the earthquake. </jats:p>

<jats:title>Parainfluenza 5 and MDA5</jats:title> <jats:p> Our immune system and the viruses that infect us are in a constant arms race, with one side always trying to outwit the other. One example is the inhibition of host protein MDA5, a member of the retinoic acid–inducible gene 1 (RIG-I)–like receptor (RLR) family of innate immune sensors, by the V protein expressed by parainfluenza virus 5 (PIV5). To better understand how this inhibition is accomplished, <jats:bold> Motz <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6120" page="690" related-article-type="in-this-issue" vol="339" xlink:href="10.1126/science.1230949">690</jats:related-article> , published online 17 January) solved the crystal structure of PIV5 V protein bound to the adenosine triphosphatase (ATPase) domain of porcine MDA5. This analysis, together with mutational studies using mouse and human versions of MDA5, revealed that the V protein unfolds the ATPase domain of MDA5 and replaces two β strands of this domain's structural core. These changes disrupt the ATPase hydrolysis site and prevent the formation of filaments by MDA5, which are important for transmitting downstream signals that activate antiviral immunity. Mutation of just two amino acids in RLR family member RIG-I also rendered this receptor susceptible to V protein–mediated inhibition. </jats:p>

<jats:title>Targeting HPV</jats:title> <jats:p> Papillomaviruses infect mammalian epithelial cells and induce cancers, including cervical cancer in humans. Vaccines against human papillomavirus (HPV) can prevent, but not cure, infection. A key viral oncoprotein, E6, acts by binding and inactivating many host proteins. <jats:bold> Zanier <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6120" page="694" related-article-type="in-this-issue" vol="339" xlink:href="10.1126/science.1229934">694</jats:related-article> ) determined high-resolution crystal structures of bovine papillomavirus bound to a peptide from the focal adhesion protein, paxillin, and of HPV bound to a peptide from the ubiquitin ligase E6AP. The structures show that the peptide binds in a pocket formed by two zinc domains and a linker helix, which represents a promising target for therapeutics. </jats:p>